Browsing by Author "Buikema, Arthur L. Jr."

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    Adolescent substance use and family dynamics
    Shilts, Lee G. (Virginia Polytechnic Institute and State University, 1988)
    The purpose of this research project was to explore the family structural variables of cohesion and adaptability as well as extracurricular activities, peer influences, and personal attitudes as they were manifested in adolescents classified as nonusers, users, and/or abusers of alcohol/drugs. Two hundred and thirty-seven adolescents responded to written questionnaires including the Alcohol and Drug Use Index, a reduced form of the Family Adaptability and Cohesion Evaluation Scales (FACES III), the Student Attitude and Behavior Questionnaire, and a Demographic Questionnaire. Information was obtained on age and grade level, gender and ethnicity, parental characteristics, and student's educational aspirations in an effort to identify factors associated with teenage alcohol/drug use. Some of the major findings suggested that the users/abusers groups reported less involvement with their families, educational pursuits, and extracurricular activities when compared to their nondrug using counterparts. The statistical analysis also confirmed some aspects of structural family therapy theory and refuted other aspects. The results of this study were also compared to prior research on adolescent substance use. These results further expanded the understanding of factors associated with adolescent use/abuse of alcohol/drugs.
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    Advanced Placement and College Success in Freshman and Sophomore Level Biology Courses
    Evans, Jackson Allan (Virginia Tech, 2009-03-16)
    This investigation examines college success in freshman and sophomore level biology courses for students with biology AP credit by addressing the following questions: One, Does AP biology experience increase academic performance in freshman biology? Do AP students with scores of 3 significantly outperform non-AP students? Do AP students with scores of 5 significantly outperform non-AP students in sophomore level biology courses? Two groups of college freshman and sophomores, those with AP biology scores and those without, were matched in regards to gender and SAT scores and instructor of record. Results suggest that students with biology AP scores of 3 may not, as suggested by the College Board, be adequately prepared to enroll directly into sophomore level biology courses. Results from this dissertation suggest the following implications: (a) AP students with final AP exam scores of 1 and 2 have derived little if any benefit from their yearlong AP biology course and the AP final exam in regards to Freshman Biology I; (b) AP biology students with scores of 3 and 4 on their end-of-the-year biology AP exam appear to be well prepared to be successful, based on mean final grades, in Freshman Biology I; (c) There is no supporting evidence that suggests AP students with AP final exam scores of 3 or 4 are adequately prepared to enroll directly into sophomore level biology courses and be successful; and (d) AP students with scores of 5 who have enrolled directly into sophomore level biology courses did not significantly outperform, based on mean final grades, non-AP students who have taken the two semester sequence of freshman biology courses. Further research needs to be done at each college and university participating in the Advanced Placement program to set appropriate cut off scores for the end-of-the-year AP exam score in regards to awarding college credit. Moreover, a considerable amount of research carried out thus far fails to capture many of the variables known to be associated with college success. Therefore, further research done in this area needs to control for these other variables.
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    Alteration and recovery of a stream macroinvertebrate community exposed to fly ash effluent and an analysis of the causative factors
    Specht, Winona L. (Virginia Polytechnic Institute and State University, 1985)
    Structural and functional changes in the macroinvertebrate community of a fly ash receiving stream were investigated during the final year of fly ash basin operation and for 10 months after fly ash discharges to the stream were terminated. Minimal changes were observed in the benthic community until the basin reached 77% of capacity, at which time the number of macroinvertebrate taxa, density of organisms, diversity, and relative abundance of Ephemeroptera all declined sharply. Ephemeroptera (mayflies) exhibited the greatest sensitivity to the fly ash effluent, while the beetle, Psephenus herricki (Coleoptera) was very resistant to the effects of fly ash. Recovery responses of the macroinvertebrate community were observed one month after fly ash discharges to the stream ended, while full recovery required 10 months. Based on the results of the field study, the toxicity of fly ash constituents (fly ash particulates, pH excursions, and heavy metals) was examined in three species of aquatic insects: Stenonema pudicum (Ephemeroptera), Hydropsyche slossonae (Trichoptera), and Psephenus herricki. Fly ash particulates were not acutely toxic to the three species at concentrations of 4000 mg/l. Stenonema pudicum was consistently the most sensitive species to acidic and alkaline pH extremes and heavy metals (Cd, Cr, Cu, Zn, and a metal mixture), while Psephenus herricki was consistently the most resistant species tested. Alkaline pH extremes and elevated heavy metal concentrations are believed to be responsible for the observed changes in the macroinvertebrate community of the receiving stream during the final two months of basin operation, while elevated heavy metal concentrations were responsible for earlier perturbation of the stream community.
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    An analysis of the job satisfaction of substance abuse counselors certified by the Commonwealth of Virginia
    Evans, William Nelson (Virginia Tech, 1993-05-15)
    Licensed substance abuse programs in the Commonwealth of Virginia are reporting turnover rates for counselors of up to 60%. Studies have indicated that low job satisfaction can be a cause for turnover in the human services professions. The entire population of substance abuse counselors certified by the Commonwealth of Virginia was surveyed by mail, using a Modified Minnesota satisfaction Questionnaire and an Individual Information Form. Of the 496 possible responses, 365 were returned for a return rate of 73.7%. The study was conducted to answer three research questions concerning the job satisfaction of these counselors and to provide insight into the possible causes of the high turnover rates. The answers to these questions sought to describe and examine the level of job satisfaction, the sources of job satisfaction and the relationship between job satisfaction and clinical supervisor and clinical supervision variables for this population. The results of the study indicate that these counselors are very satisfied with their jobs. The sources of the greatest influence on job satisfaction are represented by the scales Social service, Moral values and Creativity. The scales Advancement, Policy and practices and Compensation were the least influential on job satisfaction. A model of ten Clinical supervisor and Clinical supervision variables was regressed on job satisfaction. Four variables, Hours of supervision per week, Length of time clinical supervisor has been a clinical supervisor, Degree status of the clinical supervisor and Clinical supervisor is also the administrative supervisor were found to explain a significant amount of the variance in job satisfaction. Although these counselors indicated that they were very satisfied with their jobs, in the next five years 58.44% plan to leave their jobs, which includes 17.75% who plan to leave the substance abuse field entirely.
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    Aquatic microbial community responses to stress: comparison of nontaxonomic and taxonomic indices
    Toczydlowski, David G. (Virginia Tech, 1985-05-05)
    Three nontaxonomic indices; ATP/Chlorophyll a(ATP/Chla), ATP/ADP, and Chlorophyll a/Pheopigment (Chla/Pheo) were compared to the taxonomic measures of species diversity (d) and species richness as indicators of stress in aquatic environments. Field and laboratory microcosm responses of indigenous microbial communities exposed to municipal sewage treatment plant (STP) effluent were monitored. The STP effluent produced increased adenylate concentrations, ATP/ADP and ATP/Chla ratios, and decreased Chla, Chla/Pheo, d, and species richness relative to upstream reference communities. Nontaxonomic responses were consistent in four separate field tests. Significant differences in responses were discernible in 3 d when communities were transferred from reference to polluted sites. Chla/Pheo decreased more rapidly than other measurements. The predictive capability of laboratory flow through microcosm tests was examined by simultaneously transferring communities from upstream reference sites to downstream field sites and to various dilutions of field effluent in the laboratory.
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    Behavioral Investigation of the Light-Dependent Magnetoreception Mechanism of Drosophila melanogaster
    Dommer, David H. (Virginia Tech, 2008-04-25)
    Use of a magnetic compass has been demonstrated in all major classes of vertebrates as well as several classes of invertebrates, and is proposed to involve a photo-induced radical pair mechanism (RPM). My dissertation research consisted of characterizing a magnetic compass in a model species, Drosophila melanogaster. Preliminary experiments were carried out with adult flies, however, due to the behavioral complexity of adult responses a new behavioral assay of magnetic compass orientation was developed using larval Drosophila that elicits a robust magnetic compass response in a trained magnetic direction. This manuscript describes experiments that were conducted showing that larval magnetic compass orientation: 1) demonstrates a complex 3-dimensional pattern of response consistent with a RPM; 2) is consistent with a receptor mechanism that utilizes short- and long-wavelength antagonistic photopigments, proposed to explain wavelength dependent effects in vertebrates (e.g. amphibians and birds); and 3) produces axially symmetrical patterns of response with respect to the geomagnetic field. Additionally, tests of adult Drosophila under low and high intensities of monochromatic long wavelength light revealed a similar behavioral response to varying intensities of monochromatic light as previously reported in migratory birds (E. rubecula). These findings indicate that the magnetic compass of larval Drosophila shares a common functional architecture and similar biophysical mechanism with that of at least some vertebrates (e.g. amphibians and possibly birds), suggesting that the magnetic compass of modern vertebrates may have evolved once in a common ancestor of these three lineages over 450 million years ago. Furthermore, findings indicating a spontaneous preference for magnetic directions in D. melanogaster larvae suggest that a light-dependent magnetoreception mechanism is more widespread in insects than was previously suspected. The development of a behavioral assay to study the light-dependent magnetic compass in an organism with a simple nervous system, a limited behavioral repertoire, and with the possibility of using the full power of modern molecular and genetic techniques holds considerable promise to increase our understanding of the biophysical mechanism(s) and neurophysiological structures underlying magnetic orientation in terrestrial animals.
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    A comparison of teams-games-tournaments (TGT) and traditional classroom methods in high school biology
    Dechow, Rebecca Ross (Virginia Polytechnic Institute and State University, 1983)
    Since 1970, researchers at Johns Hopkins University have studied the effects of a game technique called the tearns-games-tournament method on the achievement scores, attitudes, and classroom process of elementary and junior high students. Their findings raised many questions about the applicability of team-games to affect achievement at the high school level or in subject areas other than math and English. In 1980, the National Science Foundation allocated funds for the creation of TGT materials for seventh-grade science, even though research of its effectiveness for science courses had not been conducted. This study was designed to provide answers to the following questions: Would high school students playing teams-games-tournaments have greater academic achievement in a high school biology course than students in classes using traditional classroom methods? Would high school students in TGT classes have greater retention of knowledge after a delayed period of time than those students in classes using traditional classroom methods? Would high school students in TGT classes have more positive attitudes toward the subject of biology than students in classes using traditional classroom methods? Would high school students like TGT better as a means for studying chapter material than traditional methods? Eight biology classes were involved in the seven-week treatment period. Analysis of variance was used to compare control and experimental groups for (1) pre-test cognitive knowledge, (2) post-test cognitive knowledge, (3) delayed post-test cognitive knowledge, (4) pre-test attitudes towards biology, and (5) post-test attitudes towards biology. Analysis of covariance was computed using I.Q. and pre-test scores as covariates for post-test cognitive means and delayed post-test cognitive means. A dependent t-test was computed for attitudes of experimental classes towards team-games. TGT had no significant effect on the biology achievement scores or attitudes towards biology of high school students in this study. Experimental classes did like team-games and sustained their attitudes towards them for the duration of the study.
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    A comparison of techniques for estimating the hazard of chemicals in the aquatic environment
    Niederlehner, Barbara R. (Virginia Polytechnic Institute and State University, 1984)
    Estimates of the concentration of cadmium constituting a threat to aquatic ecosystems were derived from laboratory tests conducted at two levels of the biological hierarchy. A population level estimate was derived from single species toxicity tests and a community level estimate was derived from laboratory tests on microbial communities. Estimates were compared to each other and to an ecosystem level estimate derived from reports of ecological health and ambient cadmium levels in rivers, lakes, and streams. Estimates of permissible levels for short term exposures differed by an order of magnitude. Single species toxicity tests indicated that a level of 46.1 ug Cd/L would affect only 5% of taxa. The corresponding estimate from the community level test was 459.4 ug Cd/L. Similar estimates of permissible levels for chronic exposures were not significantly different (1.02 and 0.20 ug Cd/L, single species arid community level tests, respectively). Both of the laboratory derived estimates of permissible levels for chronic exposure fell within a rational range; the minimum level defined by median cadmium levels reported in healthy aquatic systems (0.05 ug Cd/L), and the maximum level defined by median cadmium levels reported in damaged aquatic systems (9.2 ug Cd/L). However, the community level estimate was obtained more efficiently, permitting an estimate of effects on diversity from a single test. Single species level tests, community level tests, and field studies each contributed unique information to hazard evaluation. Using information from all levels will strengthen predictions.
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    Comparisons of Secondary Production, Life History, and Mouthpart Functional Morphology Between Two Populations of the Amphipod Gammarus minus
    Haley, Carol J. (Virginia Tech, 1997-01-21)
    In this study, features of ecology, behavior, and functional morphology related to feeding activity of two populations of the amphipod Gammarus minus were compared. The two populations occupied different habitats, and I attempted to determine whether differences observed between the two populations were related to habitat. Annual production and life history of the populations were compared and their relationship to factors such as temperature, water-chemistry, and quantity of available organic matter were examined. Mouthpart and foregut morphology were compared between the two populations and between immature and mature amphipods with light and scanning electron microscopy. Measurements of structure were analyzed by linear regression. A behavioral study, comparing feeding of immature and mature G. minus, was conducted in the laboratory. Annual production of G. minus occupying a habitat characterized by the presence of watercress, gravel substrate, and constant temperature (Site 1) was 3.9 g/m² (95% C.I.: 3.2- 4.5), while that in the habitat characterized by leaf detritus and fluctuating temperatures (Site 2) was 1.8 g/m² (95% C.I.: 1.6-2.1). Breeding occurred throughout the year at Site 1, but there was a yearly cycle at Site 2. The greatest numbers of the smallest size classes of amphipod were present at Site 2 when the quantity of ash-free dry mass (AFDM) of wood and bark was greater than AFDM of leaf detritus. Of nine mouthpart and foregut structures studied, three, the number of cuspidate setae on outer plates of maxillipeds, the length of the dactyl on maxilliped palps, and the number of hook setae on the foregut ampullae, were found to be correlated with body length. Of these, rates of increase in maxilliped setae numbers and hook setae numbers were greater for immature than mature animals, and the number of hook setae for a given sized animal was generally greater for animals at Site 1 than Site 2. Animals presented with ground-up leaf material in the laboratory exhibited twenty-one recognizable behaviors. The frequencies of six behaviors were found to be statistically different between immature and mature animals. The differences suggest that immatures may prefer a food type or size other than that provided in the experiment.
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    Development of a test system for screening toxic substances: a comparison using organic substances
    Thomas, Carolyn L. (Virginia Polytechnic Institute and State University, 1985)
    The purpose of this research was to develop a test system for screening toxic substances by predicting their aquatic ecosystem effects. The system studied was a static, one liter microcosm with a diverse species assemblage. Teh microcosm was composed of biotic inoculum, chemically defined medium and sediment. The biotic inoculum cotained primary producers, grazers, carnivores and decomposers. The chemical medium used was Taub #82 modified by adding sodium bicarbonate. Three different types of sediment were studied: sand, clay and clay plus sand. Four organic chemicals: phenol, triethylene glycol (TEG), quinoline and naphtoquinone were evaluated with this test system. The toxicities of TEG, quinoline and naphthoquinone were compared for each sediment type. Toxicity was evluated in terms of the chemicals' effects on primary productivity and heterotrophic activity though other effects are also noted. The toxicity of the chemicals in this study was compared to those from other toxicological evaluations based on threshhold toxicity values (EC20 and LC50). The screening test sytem evaluated in this study did not demonstrate significanly different threshhold toxicity values than the other screening systems to which it was compared. The ranking of the toxicants based on EC20 values was different for the two ecosystem properties, net production and heterotrophic activity. Naphthoquinone concentration exhibited no correlation between ecosystems property values and therefore, could not be ranked. Phenol exhibited the greatest toxicity to net production immediately after the toxicant addition. Quinoline was most toxic to net production over the longer time scale. TEG exhibited the least toxicity to net production, however, TEG exhibited higher toxicity to heterotrophic activity than either quinoline or phenol. Although the type of sediment used in the nicrocosms did not change the relative toxicities of the chemicals, the microcosms with clay sediment always were observed to exhibit lower net production and higher variability. Nonparametric statistical analyses are recommended for microcosm studies because of the lack of normally distributed data. Confidence limits of 80% are recommended because of the need for biologically conservative estimates of ecosystem toxicity.
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    Development of a three-trophic level toxicity test utilizing an alga (Chlorella vulgaris), rotifer (Brachinous calyciflorus), and fish (Pimephales promelas)
    Dobbs, Michael G. (Virginia Tech, 1994-05-05)
    In this research a test system was developed that is designed as a tool to evaluate the potential hazard of chemicals to aquatic ecosystems. The system developed is a linear three-trophic level food chain consisting of an alga (Ch/ore/la vulgaris), rotifer (Brachionus calyciflorus), and fish (Pimephales promelas). The chemostat design used for the lower two trophic levels was crucial in being able to supply the top trophic level with sufficient food on a continuous basis. The system was initially evaluated using copper (Cu) and selenium (Se) as toxicants. In the copper experiments, results of a 7 day three-trophic level toxicity test were compared with a series of single species tests. The LOEC was 31.5 µg/L based on a temporary impairment of the algal population growth, with a corresponding NOEC of 16.2 µg/L. The algal population at all initially impaired treatment levels demonstrated recovery to control levels by the end of the test. Single species tests with the same species showed impairment at treatment concentrations lower than the corresponding value from the three-trophic level test. The difference in sensitivity is attributable to the fact that most of the Cu in the single species tests was in the dissolved form (approximately 80 %), whereas in the trophic level test most of the Cu was not ( < 15 % dissolved Cu). The three-trophic level Se experiment lasted for 25 days, with both short-term and long-term impacts evident. At the algal trophic level, growth was not impaired on a daily basis at any of the exposure levels (110.3, 207.7, and 396.1 µg/L Se). However, algal densities were slightly reduced at the 207. 7 and 396.1 µg Sell treatments, although not significantly different when the data was pooled across days. Rotifer populations were impaired at these same levels by day 4, and succumbed to the Se by day 7. Fathead minnow growth was also impaired at these two concentrations by day 7. In addition, sub lethal impairment of rotifer and fish growth was evident at the 110.3 pg/L level after day 20 indicating a more subtle trophic impact. Bioconcentration factors ranged between 100 and 1000 µg/L and were found to be dependent on the species, treatment, and day.
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    Development of methodology for community level toxicity testing using the fathead minnow seven day survival-growth impairment test
    Lauth, John R. (Virginia Tech, 1990-12-05)
    Single species toxicity tests are widely used to assess the potential effects of a toxicant on aquatic life. Increasingly, it is necessary to understand how the results of these tests relate to toxicant effects in natural communities. This dissertation presents the methodology and validation for a community level toxicity test that bridges the gap between single species tests and natural community responses. The research involved control of environmental parameters, improvement of feeding regimes and testing of the final community. The results are presented as four separate papers. The first paper addresses the development and validation of a standardized reconstituted water for culturing and toxicity testing of algae, cladocerans, a rotifer and two fish species. The next two papers address the substitution of the food source currently used in the fathead minnow survival-growth impairment test (Artemia) with a freshwater food source (the rotiter, Brachionus calyciflorus). Along with the alga Chlorella vulgaris (producer), B. calyciflorus (primary consumer) and the fathead minnow larvae (secondary consumer) comprise a three level food chain that was used to address trophic level interactions (feeding reduction and growth impairment) in the final phase of this research. The end result is an experimental procedure in which environmental parameters (water quality, temperature, etc.) and trophic structure parameters (Le. producer and primary consumer density) can be controlled well enough to insure that any shifts in community structure can be attributed to toxicant related effects.
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    Diatom and protozoan community analysis and colonization on artificial substrates in lentic habitats
    Stewart, Paul M. (Virginia Polytechnic Institute and State University, 1985)
    The purpose of this research was to examine the colonization process and relationship of physico-chemical parameters to diatom and protozoan communities colonizing polyurethane foam (PF) artificial substrates in lentic habitats. This was the first study to utilize multivariate techniques for comparison of protozoan and diatom communities The following hypotheses were examined in this study: 1. diatom and protozoan species accrual is similar because the organisms are approximately the same size and share similar ecological conditions, 2. protozoan assemblages are influenced by the physicochemical parameters of their environment, and 3. diatoms and photosynthetic protozoans are more closely related to the physico-chemical parameters of their environment than are the protozoans of all trophic groups. PF substrates were placed in the littoral zone of lentic habitats. Substrates were sampled through a time series and examined for their diatom and protozoan species' presence-absences. The first hypothesis was tested by using the MacArthur-Wilson equilibrium model and by fitting the data to the model by non·linear least squares regression. Protozoan species accrual fit the model in most cases, while diatom species accrual did not. The second part of the research dealt with five lentic habitats in northern lower Michigan which were sampled as described above and concurrent with organismal sampling several physico-chemical parameters were sampled. These environmental parameters included pH, alkalinity, conductivity, temperature, and concentrations of dissolved oxygen, chloride, silica, ammonia, and total and ortho-phosphate. Protozoan communities were examined using reciprocal averaging ordination. It was found that the bog and marsh had distinct communities, while the three lakes did not. Several physicochemical parameters and factors correlated significantly with axes generated by samples in species space. The final section tested the degree of relationship among diatoms, autotrophic protozoans, and protozoans to the physicochemical parameters and factors. pH had the highest correlations with the first axes for each group. Diatom communities had the greatest degree of relationship to the physico-chemical parameters, evidence for this is provided by the greatest number of correlations between ordination axes and the physico-chemical parameters and factors.
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    Distributional analysis of the freshwater mussel fauna of the Tennessee River system, with special reference to possible limiting effects of siltation
    Dennis, Sally D. (Virginia Polytechnic Institute and State University, 1984)
    Mussel studies in the Tennessee River drainage (1973 - 1982) examined ecology and distribution and investigated factors limiting to distribution. This river system presently supports 71 freshwater mussel species, 25% of which are endemic to the Cumberlandian Region. Species have been extirpated from this drainage within the past 60 years, however the number of extant species remains high. The major impact of man's activities has been reduction of available habitat. Past and present distribution records indicate that mussel species assemblages are determined by geologic history and stream size. Although some overlap of species exists among stream size categories, there is no longer a continuous gradation from one category to the next; mussels exist in isolated communities separated by nonproductive river reaches. Productive reaches supporting more than 60 mussel species once existed in habitats spanning the transition from medium to large rivers; reaches now altered by impoundment. The maximum number of species reported in recent collections from any one site in the Tennessee drainage is less than 40, which seems to be the maximum number of species niches available. Quantitative sampling reveals characteristic patterns of species dominance. Changes in species dominance and age class structure provide a better basis for evaluating changes over time than do species composition or diversity alone. Mussel density was found to be more variable than species composition, and was unrelated to species abundance. Experiments on effects of siltation indicated that silt can be a significant limiting factor to mussel distribution. Transplant studies showed that mussels transplanted into heavily silted areas exhibited poor survival over a one year period compared to mussels moved to unsilted habitats. Results indicate that siltation may interfere with reproductive activity. Laboratory experiments testing the effect of suspended silt on the uptake of C-14 tagged algae by freshwater mussels showed that suspended silt can interfere with feeding. Food uptake was reduced to approximately 50% (of control) at silt levels of 211 to 820 mg/l, and to 80% at silt levels over 1000 mg/l. It was concluded that the limiting mechanism is one of dilution of food rather than direct interference with filtration or respiration.
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    Do similar communities develop in similar sites? A test with zooplankton structure and function
    Jenkins, D. G.; Buikema, Arthur L. Jr. (Ecological Society of America, 1998-08)
    McCune and Alien (1985) asked the question "Will similar forests develop on similar sites?" and concluded that dissimilar old-growth forests had developed on similar sites due to historical factors (colonization, disturbance, etc.). We asked "Do similar zooplankton communities develop in similar ponds?" We compared zooplankton community structure and function in 12 newly constructed experimental ponds during 1 yr of natural colonization and analyzed a suite of physical-chemical variables to evaluate the assumption of environmental similarity among ponds. Ponds were similar for the measured environmental variables. However, zooplankton communities were structurally different, as indicated by analyses of species presence/absence, colonization and species accrual curves, and taxa (rotifer, copepod, cladoceran, and Chaoborus) density and biomass. Species varied widely in their colonization abilities. Zooplankton communities also differed in productivity of some taxa and community-level respiration rates. Scale was important in detecting structure and function differences among zooplankton communities. Species- and taxa-level analyses showed clear differences among communities, but community-level analyses of structure (species richness, total density and biomass) and function (productivity, respiration, and ammonia regeneration rates) could not identify distinct sets of communities. Community structure and function may be comparable in sensitivity for detecting change but need to be compared at equivalent scales. Dispersal (as evidenced by colonization history) was a regulator of new zooplankton communities, because it did not occur rapidly or uniformly among similar ponds. All zooplankton do not disperse readily. The extent to which dispersal limits older zooplankton communities is unknown, but genetic studies indicate low dispersal rates among established populations. Dispersal also regulates assemblages of organisms expected to be less vagile than zooplankton and in various ecosystems, indicating that "supply-side" and metapopulation concepts are valuable for community ecology. Priority effects may have lasting influence on subsequent community structure, depending on colonization rates and sequences. We propose explicit recognition (and careful examination) of a commonly assumed but rarely tested "quorum effect": local abiotic and biotic processes regulate communities and arrival processes do not, because potential members have already arrived. Given either priority or quorum effects, dispersal may be an important, often-overlooked process regulating community structure and function, especially when it is not rapid.
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    Ecology of benthic macroinvertebrates in experimental ponds
    Christman, Van D. (Virginia Tech, 1991-09-07)
    I studied life history parameters of 5 taxa of aquatic insects in the orders Ephemeroptera and Odonata, successional patterns over 2 years of pond development, and precision of 15 biological metrics in a series of 6 replicate experimental ponds from March 1989 to April 1990. I determined voltinism, emergence patterns, larval growth rates and annual production for Caenis amica (Ephemeroptera: Caenidae), Callibaetis floridanus (Ephemeroptera: Baetidae), Anax junius (Odonata: Aeshnidae), Gomphus exilis (Odonata: Gomphidae), and Enallagma civile (Odonata: Coenagrionidae). Growth rates ranged from 0.011 to 0.025 mg DW/d for Ephemeroptera and from 0.012 to 0.061 mg DW/d for Odonata. Annual production ranged from 5 to 11 mg DW/sampler/yr for Ephemeroptera and from 10 to 673 mg DW/sampler/yr for Odonata. Comparison of the benthic macroinvertebrate community at the end of year 1 to the benthic macroinvertebrate community at the end of year 2 showed no significant differences for community summary measures (total density, taxa richness, diversity, Bray-Curtis similarity index); however, some individual taxa densities were significantly lower at the end of year 2. Physicochemical parameters measured indicated that the ponds were oligotrophic. Submerged macrophytes colonized and became established in most of the ponds during year 2. A few noninsect taxa were not present in expected numbers, probably due to lack of efficient dispersal mechanisms. Fifteen metrics were analyzed by a statistical procedure that indicates the percent change that must occur (detection limit) to detect true differences between two means. The metrics with the lowest detection limits (usually < 20%) were taxa richness, EOT index (number of taxa in the orders Ephemeroptera, Odonata, and Trichoptera), proportion of Chironominae/Orthocladiinae, and proportion of collector-gatherers. Detection limits of < 20% on all dates were also obtained for taxa richness and EOT index metrics when analyzed using dip net samples. Density metrics only allowed detection limits of about 50% on most dates. This study provided needed information on the life history of taxa important in shallow, lentic ecosystems, ecological succession in newly created ponds, and statistically sound and ecologically meaningful metrics. This study also provides a valuable baseline for impact assessment work in experimental ponds.
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    The Effect of Dieoffs of Asian Clams (Corbicula fluminea) on Native Freshwater Mussels (Unionidae)
    Scheller, Jennifer L. (Virginia Tech, 1997-06-06)
    There is a great deal of concern about the declining freshwater mussel fauna of North America. Although deteriorating water quality and habitat degradation may account for much of the decline, it has been suggested that the exotic Asian clam, Corbicula fluminea, may be having an effect on native unionids. Negative impacts may result directly from competition or indirectly, because of Corbicula population crashes that release ammonia and reduce dissolved oxygen in the sediment. Laboratory tests were conducted to determine the relative sensitivity of native mussel and Asian clam life stages to unionized ammonia, and mussel glochidia were the most sensitive (24-hr LC50 of 0.11 mg/L NH₃-N). Juvenile and adult mussels were similarly sensitivity, with average 96-hr LC50's of 0.49 and 0.52 mg/L NH₃-N, respectively. Adult C. fluminea were the least sensitive, having an average LC50 of 0.80 mg/L NH₃-N. The EPA standard test organism, Ceriodaphnia dubia, had one of the lowest LC50's (0.07 mg/L NH₃-N) of the five species, and the fathead minnow, Pimephales promelas, had the highest (1.18 mg/L). The differing sensitivities of the various life stages are important when trying to determine the impact of an Asian clam dieoff. If a dieoff occurs at a time of year when the more sensitive life stages, such as glochidia are present, then the impact on mussel recruitment may be greater. Two miniature artificial stream tests were used to determine the effect of clam density on dieoff rate, ammonia production and dissolved oxygen levels. Only clams at the highest density of 10,000/m2 experienced 100% mortality. Unionized ammonia levels exceeded 4.0 mg/L, and dissolved oxygen levels dropped below 1.0 mg/L during the dieoff. The amount of unionized ammonia produced was twofold greater than the concentration that produced an LC50 in adult C. fluminea and ~40 times greater than the LC50 for V. iris glochidia. Factors thought to have contributed to the C. fluminea dieoff were flow rate, low dissolved oxygen levels, temperature and perhaps ammonia. A complete dieoff did not occur until flow was stopped and dissolved oxygen concentrations began to drop. One-hundred percent mortality occurred in 38 days for the first test, and 21 days in the second test. Higher water temperatures in the first test (26° C) compared to the second test (average = 21.7°C) are thought to have resulted in the faster dieoff.
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    The effect of motivational interviewing on treatment participation, self-efficacy, and alcohol use at follow-up in inpatient alcohol dependent adults
    Wertz, Jennifer S. (Virginia Tech, 1993)
    This study attempted to impact length of time in treatment, treatment participation, outcome expectancies, self-efficacy, stage of change, and alcohol use at follow-up, using a brief motivational interviewing intervention (Miller & Rollnick, 1991). The subjects were 42 alcohol dependent adult men in an inpatient substance abuse treatment program in a Veterans Administration Medical Center in southwestern Virginia. One-half of the subjects (n = 20) were randomly assigned to receive a brief motivational interviewing intervention at the beginning of the usual 28 day treatment program. Contrary to predictions, subjects who received motivational interviewing did not remain in treatment significantly longer, were not rated as significantly more involved in treatment, and did not score significantly higher in self-efficacy than subjects who did not receive the motivational interviewing intervention. Subjects who received motivational interviewing also did not use less alcohol at follow-up, 1 month after the end of treatment. In a set of regression analyses, outcome expectancies, self-efficacy, and stage of change were used to predict days in treatment and therapist ratings of treatment participation. Implications of these findings for further research incorporating motivational interviewing are discussed.
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    The effects of atrazine on nitrogen cycling in a freshwater wetland microcosm
    Wilhite, Rhonda E. (Virginia Tech, 1996)
    Atrazine and other pesticides may damage non-target ecosystems, such as wetlands, by destroying vegetation or by disrupting microbial communities and nutrient cycling. The addition of atrazine to a wetland microcosm will disrupt the nitrogen cycle by inhibiting nitrifying and denitrifying bacteria. The inhibition or absence of functional groups of bacteria will limit the ability of the wetland to remove nutrients and herbicides, thus increasing nitrogen levels in non-point source pollution. All tests were conducted in the laboratory using microcosms established from intact plant/sediment core subsamples collected from a natural freshwater wetland. Each microcosm received distilled water, atrazine, or acidified distilled water (pH 2) by groundwater seepage. Microcosms were dosed with 1.5 mg/L and 4.5 mg/L atrazine. Acid treatment of microcosms was done to provide a perturbation reference to the microcosm. Nitrite, nitrate, and ammonia levels were determined, as was dissolved oxygen, pH, and conductivity. The nitrifying bacteria and denitrifying bacteria were enumerated. Data were analyzed with one way analysis of variance (ANOVA) with block and treatment interaction and Tukey's Studentized Range test. Acid treatment of microcosms provided a positive control of microcosm disturbance. Acidification of the sediment disturbed the nitrogen cycle by suppressing ammonia dependent microbial processes. Atrazine (at 1.5 and 4.5 mg/L atrazine) did not significantly affect the number of nitrifying bacteria. The denitrifying or nitrate reducing bacteria were stimulated by exposure to atrazine and nitrate reduction became the dominant microbial process following exposure to atrazine. This shift toward denitrification and nitrate reduction processes caused increased levels of nitrite in the overflow waters. The continued accumulation of atrazine may cause nitrogen losses from an ecosystem which is already nitrogen limiting. Over time, predominant plant species may change, becoming primarily nitrogen fixing species. Changes in plant species would bring about changes in associated microbial populations. Excess nitrogen present in wetland runoff may cause algal blooms in receiving waters and pose health risks in contaminated drinking water. Accumulation of atrazine in wetlands may, ultimately, result in the loss of buffer zones.
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    Effects of forest disturbance on shredder production in headwater streams
    Stout, Benjamin Mortimer (Virginia Tech, 1990)
    Effects of forest disturbance on leaf shredding aquatic insects were investigated by comparing leaf biomass and shredder production in disturbed versus reference forest streams. Benthic samples were collected monthly in 3 streams in a mature hardwood reference forest and 3 streams in an 11-year-old clearcut. Reference forest streams had significantly greater total leaf biomass and significantly more slow-processing leaf material than disturbed forest streams. Disturbed forest streams had significantly greater fast-processing leaf biomass than did reference streams. The leaf shredding insects Tipula abdominalis, Pycnopsyche sp., and Tallaperla maria comprised over 90% of the shredder biomass in all streams. Total shredder production was Significantly greater (p<0.05) in disturbed versus reference streams. Production of Pycnopsyche and T. maria was significantly greater (p <0.10) in disturbed versus reference streams, but T. abdominalis production was not significantly different (po =0.28). Greater T. maria production was attributed mostly to better survivorship in disturbed versus reference streams. Greater total shredder production in disturbed streams was attributed mostly to greater production by Pycnopsyche, which was due mostly to better survivorship and growth of early instar larvae in disturbed streams. T. maria and T. abdominalis were studied under laboratory conditions to determine whether feeding on various types of leaf material would affect growth. Shredder growth rates were affected more by length of instream conditioning of leaves than leaf species or leaf exposure site. Each shredder species had different patterns of growth and survivorship relative to leaf species and conditioning. There was no difference in shredder growth patterns between early versus late successional leaf species. Pycnopsyche growth was not studied, but Pycnopsyche may be more capable than the other shredders of exploiting fast-processing, early successional leaf species. Pycnopsyche production was greatest in streams having the greatest quantities of early successional leaf biomass. Pycnopsyche biomass correlated significantly with fast-processing leaf biomass typical of the early successional forest, whereas other shredders did not. Shredder production was significantly greater in disturbed versus reference forest streams, even though total leaf biomass was significantly greater in reference streams. Providing that forest clearcutting is accomplished with minimal physical disturbance to streams, shredder populations may exhibit greater production in streams 11-years after forest clearcutting than in reference forest streams.